Liquid electrophotographic developers

ABSTRACT

A LIQUID TONER COMPOSITION COMPRISING AN ELECTRICALLY INSULATING CARRIER LIQUID, A PIGMENT AND A COPOLYMER OF MALEIC ANHYDRIDE AND A HIGHER ALKYL INYL ETHER. THE ALKYL GROUP OF THE ALKYL VINYL ETHER CONTAINS FROM ABOUT 16 TO ABOUT 22 CARBON ATOMS.

United States Patent Oflice 3,776,849 Patented Dec. 4, 1973 US. Cl. 25262.1 8 Claims ABSTRACT OF THE DISCLOSURE A liquid toner composition comprising an electrically insulating carrier liquid, a pigment and a copolymer of maleic anhydride and a higher alkyl vinyl ether. The alkyl group of the alkyl vinyl ether contains from about 16 to about 22 carbon atoms.

This application is a continuation in part of copending application Ser. No. 875,515, filed Nov. 10, 1969, now abandoned.

The present invention relates to a liquid toner composition for use in electrostatic printing processes.

Although a great number of liquid toner compositions or systems for use in electrostatic printing processes have been disclosed, many of such compositions or systems have not been found completely satisfactory in view of their inability to remain in suspension adequately or to give copies which have uniform fill and are free from bleeding or similar streaking characteristics.

With respect to electrophotographic processes in general, it is known that various liquid developing agents or toners are capable of producing electrophotographic images on photoconductive surfaces in various colors. Thus, for example, if the photoconductive surface comprises zinc oxide, which substance supports a negative electrostatic charge, it is necessary for the developer particles suspended in a liquid carrier to assume positive polarity with respect to the latent electrostatic image formed on the zinc oxide surface.

Various types of positive-working electrostatic toners have been formulated to eliminate the disadvantages and deficiencies of the prior art. These formulations require the use of a charge control agent such as a heavy metal salt. The typical such salts are salts of copper, cobalt or zinc. Many of these formulations are slow-drying and give dirty white areas.

It has now been found in accordance with the present invention that excellent electrostatic developers free from the disadvantages and deficiencies of the prior art materials are provided by a system comprising an electrically insulating carrier liquid, a pigment such as carbon black and a copolymer of maleic anhydride and a higher alkyl vinyl ether. The copolymer combines the properties ordinarily imparted to such a composition of the dispersing agent, the fixing agent and the charge control agent. In particular, it has been found that a copolymer of maleic anhydride and a higher alkyl vinyl ether, wherein the alkyl group contains from about 16 to about 22 carbon atoms, prepared by the addition of the maleic anhydride to the higher alkyl vinyl ether is especially useful.

Accordingly, it is a primary object of the present invention to provide an electrostatic toner or developer free from the inherent disadvantages and deficiencies of prior art compositions or systems.

It is a further object of the present invention to provide an improved electrophotographic developer which produces a self-fixing, fast-drying image.

It is still another object of the present invention to provide an improved electrophotographic developer which produces a high density image with clean, white areas.

It is yet another object of the present invention to provide an improved positive-Working electrophotographic developer which comprises a copolymer combining the action of the dispersing agent, the fixing agent and the charge control agent.

Still further objects and advantages of the present invention will become more apparent from the following more detailed description thereof.

The above objects and advantages of the present invention are provided by a liquid positive-working electrostatic toner comprising an electrically insulating carrier liquid, containing a pigment such as carbon black and a copolymer of maleic anhydride and one or a mixture of several higher alkyl vinyl ethers, ha-ving alkyl groups containing from about 16 to about 22 carbon atoms. The preferred copolymer is a copolymer of about one mole of maleic anhydride and about one mole of n-octadecyl vinyl ether.

In accordance with a preferred aspect of the present invention, it has been found that maleic anhydride-higher alkyl vinyl ether copolymers which have been prepared by the addition of about one mole of the maleic anhydride to about one mole of one or a mixture of higher alkyl vinyl ethers are especially useful due to their enhanced solubility in hydrocarbon solvents. These copolymers may be prepared by conventional methods, for example, by copolymerizing maleic anhydride and a higher alkyl vinyl ether in a solvent solution using an organic free-radical generating initiator. At the completion of the polymerization reaction, the precipitated copolymer can be isolated by any suitable means, such as filtration, washed with fresh solvent and vacuum dried.

The amount of solvent is not critical and the solvent chosen should be a suitable medium for both of the monomers. Such solvents as benzene, toluene, xylene, acetone, cyclohexane, saturated petroleum products, methylethyl ketone and methylene chloride and the like as well as mixture thereof may be used. A particular solvent which is especially useful is Humbles Isopar G, which is an isoparafiinic petroleum hydrocarbon fraction, having an average molecular weight of 146 and a boiling range of 318-345 P. (160-165" C.). Generally, the solvent used should have a boiling point range of from about to about 250 C.

Among the organic free-radical generating initiators that may be used are azobisisobutyronitrile, benzoyl peroxide, lauroyl peroxide, caprylyl peroxide, acetyl peroxide, butyryl peroxide, acetyl benzoyl peroxide, succinyl peroxide, di-tert-butyl peroxide or dimethyl azoisobutyrate and the like. Mixtures of these catalysts are also suitable for making these copolymers. Additionally, radiation polymerization can be utilized using such high energy radiation sources as ultraviolet light, X-rays and the like.

The polymerization may be carried out at a temperature within the range of 0 to about 150 C.

Examples of the various higher alkyl vinyl ether monomers which may be used are:

hexadecyl vinyl ether octadecyl vinyl ether eicosyl vinyl ether docosyl vinyl ether and the like, as well as mixtures thereof.

Thus, in accordance with the present invention, the liquid toner composition or system comprises as a base fluid any of the conventional electrically insulating carrier liquids generally employed in liquid developer and toner compositions. Such electrically insulating carrier liquids generally comprise hydrocarbon solvent materials having the necessary dielectric constant, e.g. less than 3, and volume resistivity, e.g. in excess of 10 ohm centimeter, so as to be acceptably employed in the electrostatic reproduction process. Thus, for example, the solvent can comprise various hydrocarbon solvents, as well as various commercial petroleum and hydrocarbon solvents, such as Isopar G having a boiling range of about 160175 C., or Solvesso 100 having a boiling range of about 160-174" C.

The coloring agent or pigment employed in accordance with the present invention can comprise any of those conventionally employed in electrostatic toners. Thus, for example, the pigment can comprise carbon black, channel black or the like. The pigment, for instance carbon black, suspended in the carrier liquid as the toner is employed in that amount necessary when attracted to the negative electrostatic image through the positive-working of the copolymer in the toner system to be deposited on the image areas only and provide the desired positive print or copy. In general, the pigment is present in a ratio with the copolymer of from about 2.5-1 to about 1-40. As previously indicated, when using the composition of the present invention which includes a maleic anhydridehigher alkyl vinyl ether, wherein the alkyl group contains from about 16 to about 22 carbon atoms, it is unnecessary to include modifiers such as metal soaps or salts.

The present invention will now be described by reference to the following specific examples. It is to be understood that such examples are presented for purposes of illustration only, and the present invention is in no way to be taken as limited thereto.

EXAMPLE I The following materials were mixed together:

200 ml. Isopar G 5 g. Witco Continex EPF Carbon Black 50 g. Gantrez AN 8194 (a copolymer of one mole noctadecyl vinyl ether and one mole maleic anhydride as a 40% solution in toluene).

This mixture was irradiated for 20 minutes at 75 F. in a Blackstone 500 watt ultrasonic dispersing unit to disperse the carbon black in the resin solution. 7 cc. of the resulting toner concentrate were diluted up to 1 liter with Isopar G to obtain a toner dispersion usable in the regular office copying machines. The optical density of the dispersion was approximately 7.

A copy was made by exposing a zinc oxide coated sheet to form a negatively charged image and immersing the same into the dispersion as prepared in this example. A positive reproduction of the original was obtained. The copy was of good quality, i.e. there was no background, there was good image filled with high black print density and the image was sharp and very smudge resistant.

The dispersion did not show any tendency to settle out or to agglomerate.

EXAMPLE II The procedure of Example I was repeated using a carbon/resin ratio of 2.5-1 and equally good reproduction was obtained EXAMPLE III The procedure of Example I was repeated using a carhon/resin ratio of 1-1. A good, clear, positive reproduction of the original was obtained, as in Example I.

EXAMPLE IV The procedure of Example I was again repeated using a carbon/resin ratio of 1-2. Again, a good reproduction was obtained.

EXAMPLE V A dispersion was made following the procedure of Example I using a carbon/resin ratio of 1-4. Again, a good quality positive reproduction of the original was obtained.

4 EXAMPLE VI The procedure of Example I was again repeated using a carbon/resin ratio of 1-8. The positive reproduction of the original which was obtained was of good quality.

EXAMPLE VII A dispersion was made according to the procedure of Example I using a carbon/resin ratio of 1-20. Again, a good quality copy was obtained.

EXAMPLE VIII The procedure of Example I was again followed using a carbon/ resin ratio of 1-40. As in Example I, a positive reproduction of the original was obtained having a good quality.

EXAMPLE IX Following the procedure of Examples I through VII, dispersions were made using Columbian Carbon Lampblack #8 instead of Continex EPF Carbon Black. In each instance, a good quality positive reproduction of the original was obtained.

EXAMPLE X Following the procedures of Examples I through VII, dispersions were made using Columbian Carbon Channel Black No. 999 instead of Continex EPF Carbon Black. In each instance, a good quality positive reproduction of the original was obtained.

EXAMPLE XI Example I is repeated by using a dispersion containing Milori Blue (CI. Pigment Blue 27) instead of Continex EPF Carbon Black. A blue colored positive reproduction of the original is obtained.

EXAMPLE XII Example XI is repeated using Alkali Blue (C.I. Acid Blue 119) in place of Milori Blue. A blue positive image of good quality is obtained.

EXAMPLE XIII Example XI is repeated using Pigment Green B (CI. Pigment Green 8) in place of Milori Blue. A green positive image of good quality is obtained.

EXAMPLE XIV Example XI is repeated using Permanent Carmine F (CI. Pigment Red 5) in place of Milori Blue. A carmine positive image of good quality is obtained.

EXAMPLE XV Example XI is repeated using Anthragen Red Violet RH (C.I. Vat Violet 2) in place of Milori Blue. A red positive picture of good image quality is obtained.

EXAMPLE XVI Example XV is repeated using Hausa Yellow GR (CI. Pigment Yellow 2) in place of Anthragen Red Violet. A yellow positive picture of good image quality is obtained.

The preceding Examples I to XVI show the ability of the electrostatic liquid toner of my invention to convert a negatively charged latent image into a visible image, thereby demonstrating that a positive charge is imparted 'by the maleic anhydride-vinyl ether copolymer to the pigment particles. Thus, one obtains with negatively charged zinc oxide layers a positive image from a positive original or a negative from a negative. However, when using positively charged electrophotographic layers the toner composition of my invention produces a reversal type image as illustrated by the following example:

EXAMPLE XVII A commercially available electrophotographic printing plate consisting essentially of an aluminum support on which 15 coated a layer containing a mixture of an organic photoconductor such as 2,5 bis-[4-diethylaminophenyl (1') ]-l,3,4-oxadiazole and an insulating binder resin, e.g. a polyindene resin, ketone resin or phenol-formaldehyde resin optically sensitized by Cristal Violet, Brilliant Green, or Rhodamine B, is charged positively and exposed through a positively reading transparent original. Upon development with any of the toners described in Examples I to XVI one obtains a reversal image of the original, namely, a negatively reading copy of the original. When the positively charged electrophtographic plate is exposed through a negatively reading original, a positively reading copy of the copy is obtained.

Additional refinements are within the scope of my invention. For example, sometimes a very high degree of smudge and smear resistance of the final image is required. Then the use of a so-called film-forming resinous fixing agent becomes necesary.

This film-forming fixing agent must not only be entirely soluble in the liquid vehicle, but must also possess a good ability to release the solvent by complete and rapid evaporation to permit the formation of a coherent solid deposit in film form as the evaporation residue of the solution. The film thus deposited must be non-tacky, adhesive and coherent so that the final image formed does not smudge nor smear. Furthermore, the film-forming agent must not cause the deterioration of the positive charge on the particle imparted by the proposed copolymers.

Suitable film-forming fixing agents include solid resin esters, e.g. diethylene glycol ester of rosin, glycerol ester of modified rosin, pentaerythritol ester of rosin, pentaerythritol ester of polymerized rosin, modified pentaerythritol ester of rosin, pentaerythritol ester of hydrogenated rosin, pentaerythritol ester of dimeric rosin acids, glycerol ester of polymerized rosin, glycerol ester of hydrogenated rosin, rosin-modified phenol-formaldehyde resin, rosinmodified phenol-formaldehyde resin and rosin-modified maleic anhydridepolyhydric alcohol resin. Such materials are commercially available under the trade names Pentalyn (Hercules) and Amberol (Rohm & Haas). The use of such a material is illustrated by the following example:

EXAMPLE XVIII The following materials were mixed together:

200 ml. Isopar G 5 g. Witco Continex EPF Carbon Black g. Hercules Pentalyn H (a pentaerythritol ester of hydrogenated rosin) 50 g. Gantrez AN 8194 (a copolymer of one mole n-octadecyl vinyl ether and one mole maleic anhydride as a 40% solution in toluene).

This mixture was irradiated for minutes at 70 F. in a Blackstone 500 watt ultrasonic dispersing unit to disperse the carbon black in the resin solution. 7 cc. of the resulting toner concentrate were diluted up to 1 liter with Isopar G to obtain a toner dispersion usable in the regular ofiice copying machines. The optical density of the dispersion was approximately 7. The dispersion did not show any tendency to settle out or to agglomerate.

A copy was made by exposing a zinc oxide coated sheet to form a negatively charged image and immersing the same into the dispersion as prepared in this example. A positive reproduction of the original was obtained. The copy was of good quality, i.e., there was no background; there was good image fill with high black print density; the image was sharp and extremely snudge and smear resistant.

What is claimed is:

1. A positive-working electrostatic liquid toner comprising:

(a) an electrically insulating carrier liquid having a dielectric constant of less than 3 and a volume resistivity of greater than 10 ohm cm.;

(b) a pigment; and

(c) a copolymer of about one mole maleic anhydride and about one mole of one or a mixture of higher alkyl vinyl ether wherein the alkyl group of said ether contains from about 16-22 carbon atoms.

2. The toner of claim 1, wherein said pigment comprises carbon black.

3. The toner of claim 1, wherein said carrier liquid is a hydrocarbon.

4. The toner of claim 3, wherein said hydrocarbon carrier liquid has a boiling range of about to about 250 C.

5. The toner of claim 1, wherein said copolymer is a copolymer of about one mole maleic anhydride and about one mole n-octadecyl vinyl ether.

6. The toner of claim 1, wherein said copolymer is a copolymer of about one mole maleic anhydride and about one mole hexadecyl vinyl ether.

7. The toner of claim 1, wherein said copolymer is a copolymer of about one mole maleic anhydride and about one mole eicosyl vinyl ether.

8. The toner of claim 1, wherein said copolymer is a copolymer of about one mole maleic anhydride and about one mole docosyl vinyl ether.

References Cited FOREIGN PATENTS 1,016,072 1/1966 GreatBritain 252'62.1

NORMAN G. TORCHIN, Primary Examiner J. P. BRAMMER, Assistant Examiner 

